Primary Lateral Sclerosis (PLS) is a group of rare, degenerative, neurological disorders. They are sporadic, meaning there is no clear familial link, although there are hereditary forms of PLS.
PLS is caused primarily by degeneration of the upper motor neurons in the brain and spinal cord, which results in increasing spasticity and weakness of voluntary muscles. It is often referred to as a benign variant of Amyotrophic Lateral Sclerosis (
The disorder usually begins in the legs but can begin in the upper body or bulbar (speech and swallowing) muscles. The age of onset is generally between 35 and 66 years of age, with a median age of 50.
The incidence rate for PLS is difficult to determine. One study puts it at 500 individuals in the United States. However, many researchers feel this is inaccurate, and that the actual incidence rate is closer to 2000. The issue is further complicated by the fact that researchers also believe a good portion of those initially diagnosed with PLS may actually have
Here's a quick overview Chart.